[rules-dev] RFC: declaration syntax

[Michael Anstis]

Personally, I don't see a problem with option 1.

For consistency (with entry-points) the named windows and usage thereof
should, IMO, be defined thus:-
*
*
**declare window X
    @type( tumbling )
    @keep( last 10 )
    StockTick( symbol == "RHT" ) from entry-point Y
end

rule Z
when
    StockTick() from window x
then
    ...
end

I assume the window declaration supersedes "over window:length" and "over
window:time", since the semantics seem to be defined in the declaration.

Please let me know when this is closer to reality as Guvnor will need to
support this.

Cheers,

Mike

On 26 July 2011 20:28, Edson Tirelli <ed.tirelli at gmail.com> wrote:

>
>    All,
>
> BACKGROUND:
>    As Drools moves forward, we need to be able to declare several new
> structures, as well as make existing structures more robust for compile time
> analysis, error reporting and tooling support. For instance, as it is today,
> entry points are implicit declared by simply using them, i.e., if someone
> writes a pattern:
>
> X() from entry-point Y
>
>    The engine will create entry-point Y implicitly. This is easy to use,
> but this makes it impossible for the engine to detect typos and report
> during compilation time. So, the idea is that we will allow the user to
> declare all the entry points he wants to use in his application and we will
> have a configuration option to enforce or not that list of declared entry
> points. If the configuration is set to enforce and the engine finds a rule
> that is using an entry point that is not part of the list, the engine can
> raise a compile time error point out the user's mistake. E.g., using pseudo
> code:
>
> declare entry-point X, Y
> declare entry-point Z
>
>    Drools also needs a way to declare named windows for re-use on multiple
> rules. For instance, using pseudo code:
>
> declare window X
>     @type( tumbling )
>     @keep( last 10 )
>     StockTick( symbol == "RHT" ) from entry-point Y
> end
>
>   And in the rule:
>
> rule Z
> when
>     StockTick() from window:named X
> then
>     ...
> end
>
> QUESTION:
>    As we can see above, we will need several new constructs in order to
> support features in our roadmap. We have the choice of making them all top
> level constructs, making the error recovery in the parser a lot more
> complicated, or we can re-use our declare construct to define these new
> structures as I presented in the pseudo-code above. Any pros/cons you can
> see in such approach?
>
> OPTION 1 (more verbose, but simpler and more stable):
> <epDeclaration> ::= declare entry-point <epName> [, <epName]*
> <windowDeclaration> ::= declare window <windowName>
> <restOfTheWindowDeclaration> end
> <typeDeclaration> ::= declare [type] <typeName> <restOfTheTypeDeclaration>
> end
>
> OPTION 2 (makes error recovery harder, but it is less verbose):
> <epDeclaration> ::= entry-point <epName> [, <epName]*
> <windowDeclaration> ::= window <windowName> <restOfTheWindowDeclaration>
> end
> <typeDeclaration> ::= declare <typeName> <restOfTheTypeDeclaration> end
>
> OPTION 3:
> <epDeclaration> ::= someOtherKeyword entry-point <epName> [, <epName]*
> <windowDeclaration> ::= someOtherKeyword window <windowName>
> <restOfTheWindowDeclaration> end
> <typeDeclaration> ::= declare [type] <typeName> <restOfTheTypeDeclaration>
> end
>
>
>    Edson
>
> --
>   Edson Tirelli
>   JBoss Drools Core Development
>   JBoss by Red Hat @ www.jboss.com
>
> _______________________________________________
> rules-dev mailing list
> rules-dev at lists.jboss.org
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>
>
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